This invention relates to an optical lens for use in an optical head for reading an optical disk, and in particular, to a lens coating in relation to a high-precision mounting of an optical lens to an optical head with a use of a reflected light of a laser beam from a lens.
In a conventional optical lens for use in an optical head for reading an optical disk, a reflection preventing coating (hereinafter referred to also as a coat) is provided at each of a light-incident surface into which light comes and a light-outgoing surface from which the incident light is emitted and a laser beam of 780 nm is used as a passing light for the lens. Further, the optical characteristic of the reflection preventing coat provided on each of the light-incident surface (S1) and the light-outgoing surface (S2) of an optical lens is such one as shown in FIG. 1.
FIG. 1 is a drawing for explaining a conventional example of a coat (reflection preventing coat); FIG. 1(a) is an illustration of the layer structure of the coat on the surface S1 and the surface S2, and FIG. 1(b) is a drawing showing the reflectance (spectral reflectance) vs. the wavelength of light.
Moreover, the reflectance R (%) on the ordinate in FIG. 1 and in FIG. 2 to FIG. 7 which are described below is represented in logarithmic scale for the convenience of preparing the drawings. (Only in the last FIG. 8, the ordinate is represented with divisions of equal intervals.)
The layer structure of the reflection preventing coat of the light-incident surface (S1) and the light-outgoing surface (S2) (for light having a wavelength of 780 nm) is made such one as stated below. Further, for a substrate material, a resin material such as an acrylic resin, xe2x80x9cArtonxe2x80x9d resin, xe2x80x9cZeonexxe2x80x9d resin, or a polycarbonate resin is used.
First layer: cerium oxide (refractive index nxe2x89xa02.03) layer thickness dxe2x89xa034 nm
Second layer: silicon oxide (refractive index nxe2x89xa01.45) layer thickness dxe2x89xa0177 nm
With respect to the position adjustment in mounting an optical lens to an optical reading head, a lens which has been coated with reflection preventing coats is fitted in an optical reading head, and a Hexe2x80x94Ne laser beam having a wavelength of 633 nm is irradiated through this lens, and the position adjustment is done by utilizing the reflected light.
However, as shown in FIG. 1, the reflectance for the wavelength 633 nm of a Hexe2x80x94Ne laser beam is as low as 4.3%, and there has been the problem that a high precision can not be obtained in the position adjustment of the lens.
This invention has been made in order to solve the above-mentioned problem. That is, it is an object of the invention to provide means for improving the precision of the position adjustment of the lens, by preventing the lowering of the intensity of transmitting light having the wavelength (xcexT) and by raising the reflectance of the surface S2 for the wavelength (xcexR) of the light for the position adjustment.
The object of this invention can be accomplished by employing any one of the structures described below.
That is, in an optical lens to be used for a passing light having the maximum intensity at the wavelength (xcexT) 780xc2x110 nm, an optical component is made such that both or at least one of a light-incident surface (S1) and a light-outgoing surface (S2) is provided with a reflection preventing coating and the following inequality is satisfied:
R2(xcexR) greater than R1(xcexR),
where R1(xcexR) and R2(xcexR) denote the reflectance of the respective surfaces for a light having a wavelength (xcexR) falling within a range from 500 to 700 nm.
Further, in an optical lens to be used for a passing light having the maximum intensity at a wavelength (xcexT) falling within a range from 600 to 700 nm, an optical component is made such that both or at least one of the light-incident surface (S1) and the light-outgoing surface (S2) is provided with a reflection preventing coating, and the following inequality is satisfied:
R2(xcexR) greater than R1(xcexR),
where R1(xcexR) and R2(xcexR) denote the reflectance of the respective surfaces for a light having a wavelength (xcexR) falling within a range from 750 to 850 nm.
Further, in an optical lens to be used for a passing light having the maximum intensity at a wavelength falling within a range from 350 to 500 nm, an optical component is made such that both or at least one of the light-incident surface (S1) and the light-outgoing surface (S2) is provided with a reflection preventing coating, and the following inequality is satisfied:
R2(xcexR) greater than R1(xcexR),
where R1(xcexR) and R2(xcexR) denote the reflectance of the respective surfaces for a light having a wavelength (xcexR) within a range from 500 to 800 nm.
Further, the reflectance R2(xcexR) of the light-outgoing surface (S2) of the optical component is made not smaller than 5% for the wavelength (xcexR).
For example, these are as follows.
(1) When the transmittance T(xcexT) for a laser beam having a peak intensity at the wavelength (xcexT) 780 nm is made 96% or more and the wavelength (xcexR) falls within a range from 500 to 700 nm, desirably is the wavelength of 633 nm of a Hexe2x80x94Ne laser beam, the following conditional formula is satisfied:
R1(xcexR) less than R2(xcexR),
where R1(xcexR) and R2(xcexR) denote the reflectance of the light-incident surface and the light-outgoing surface respectively.
(2) When a lens is fitted in a pickup for an optical disk player, light is irradiated to the surface S2 of the lens and the position adjustment in the fitting is done by detecting the reflected light. Assuming that the wavelength of the reflected light is xcexR, the yield of assembly in the fitting greatly depend upon the reflectance R2(xcexR) of the surface S2 for light having the wavelength xcexR. In the case where R2(xcexR)xe2x89xa75%, the yield of 88% or more can be obtained, and in the case where R2(xcexR)xe2x89xa77%, the yield of 95% or more can be obtained. In order to make the expense of assembly smaller as far as possible, it is necessary to raise the yield as much as possible; it is required at least that R2(xcexR)xe2x89xa75%, and it is desirably required that R2(xcexR)xe2x89xa77%.
This invention is capable of solving these requirements.